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COMMONWEALTH 




CIRCULAR No. 2. 



OF AUSTRALIA. 






Institute of Science and Industry. 

(Reprint from "Science and Industry," Vol. I.. Xo. 1. May, 1919.} 



Leaks in Fruit Containers. 



R. GREIG-SMITH, D.Sc. 

" The Tin Factory, in what might be termed its trial run, was an expensive 
experiment. In a total of 107,191 2£-lb. cans made by this Factory, and used in 
canning, 15,408 were found during processing to be leaky, and of those manu- 
factured and purchased 5,013 developed leaks in the warehouse. Besides these, 
6.959 were spoiled in manufacture, and 4.773 faulty cans were found amongst 
those purchased. These make a total loss of 14.7 per cent, of the 21-lb. cans 
used. Further, of 3,140 No. 10 cans purchased, there was a loss of 23 per 
cent, through leaks. It is still a controversial point as to where the fault 
lies, but in the light of cold fact, wherever the fault, considerable monetary 
loss has been the result.*' 

— State Industrial Undertakings (New South Wales) Report of the Auditor- 
General, 1918, p. 77. 

The quotation is interesting in showing the heavy loss that may occur in a can- 
nery, even with the most improved plant, for that at Leeton, on the Murrumbidgee 
Irrigation Area, is of the most modern type. It may be that much of the loss was 
caused by the faulty closing of the containers, for that is the weak point about 
the preservation of fruit and vegetables. Unless solder is used, no machine can 
lit on a lid and make the container absolutely air and water tight, that is, 
make it equivalent to a hermetically-sealed vessel. There is always a weakness 
where metal joins metal with a non-metallic luting material at the points of 
contact. The internal pressure developed during the processing finds out the weak- 
places, and there is leakage, with its attendant troubles. 

My attention was called to the irregularities in the canning process by one <>f 
our leading fruit-canners. who desired to know the reason for the *' springing " 
of his tins of preserved fruit. Some time after processing, the tins, which nor- 
mally should have concave ends, indicating a partial vacuum within, become 
bulged at one or both ends, clearly showing that internal fermentation has 
occurred. Such containers are condemned as containing food unfit for human 
consumption, as doubtless they do. Putting them through the boiler again, that 
is " reprocessing " them, does not do much good, as they may become worse, and 
the reason for this becomes evident when the cause of the " springing " is under- 
stood. 
C.7946. 



In processing pears, for example, the fruit is pared, halved, cored, washed, and 
filled into the empty containers, which are placed upon a travelling belt. A girl 
fills them with boiling syrup up to anything from half to a quarter of an inch 
from the top. Then they pass to the closing machine, which turns the lid on 
the cylindrical wall of the container by forming a double interlocking hook. The 
tin goes to the boiler, where it is cooked. On emergence from the boiler, the 
tins are stacked on the floor of the cannery until they are sufficiently cold to 
enable them to be taken to the storage room, where they are arranged in tiers. 
After a time many of them begin to ooze syrup from the junction around the top 
or bottom, and the leakage may continue, or it may stop, and the syrup hardens, 
forming a lute of dried syrup. It is among these that the springers are 
afterwards found. 

The " springing " results from the production of gas inside the tin. and. as 
this is unable to escape, the top is forced outwards, and the pressure may 
be so great as to cause the syrup to be forced out through the junction 
of the lid with the side of the tin. The gas must be produced by 
the action of micro-organisms, unless it be by the activity of fruit 
enzymes. The latter is unlikely, partly because of the heat to which the contents 
have been subjected during the cooking process, and partly because, if they 
were the agents, every tin would be a springer. The closed tins are put through 
a boiler, and are in the boiling water for sixteen minutes, which, according to 
laboratory experiments,* is quite enough to thoroughly pasteurize the contents. 
One should, therefore, look to the subsequent treatment for the cause of the 
trouble. We found that the active organisms were yeasts, and as these could not 
have persisted through the cooking process, it follows that they must have gained 
entry afterwards. The most plausible suggestion is that the lids are not absolutely 
sealed. Previous to fixing on, the margins of the lids are painted or dusted with 
a composition, which packs the space between the flanges when the lid is turned 
over the container side. The composition seems to vary. It consists sometimes of 
flour, dextrin, and finely powdered cork, at others of flour, dextrin, and rice starch.- 
It does not form an impervious lute, possibly because the starch and flour are 
jellified by the hot water, and blown out by the internal pressure, so that the cork 
alone remains. As nearly every second tin of pears shows signs of leakage in the 
storage room, it is evident that the closure of the tins is by no means perfect. A 
rubber composition is used by some canners, and this should make a more efficient 
lute. 

Since the closing is so imperfect, one is justified in presuming that, as the can 
cools down and the contained steam becomes condensed, there is an inward pres- 
sure or vacuum, and a certain amount of air is drawn inside the tin. This is the 
root of the trouble. Any living microbe;, yeast, or mould which chances to be in 
the air that is sucked in will destroy the sterility of the contents. If it is a yeast, 
much will depend upon its power of causing a fermentation of the syrup. Some 
yeasts produce little gas, others are active fermenters, and will produce 
" springers." If the organism is an acid-producer, the tin will become a " sour," 
which may not be of any industrial consequence. The already acid syrup may, 
with a little more acidification, which is recognisable only by the expert, become 
so unsuitable to the microbe that it is killed off, and the trouble does not become 
excessive. It is entirely a matter of chan ce as to whether any microorganism 
gets in, or that the organism, gettini in, iCjMj^km^thfe'TOTrtents. - In a cannery, 
where so much fruit is being dealtlwith, one w^uid^xpepfc^Jne yteasts that do 
obtain entry to be fruit yeasts, thatf is, the kind Tcnown as wild yejasts. It was 



* " The ' Springing ' of Tins of .tfreserv 
R. GreigrSmith, Proc. Linn. Soc, Nlw South Wales 



1918, p. 409. 



[Estrange and: 



•SOCUMficNTS DIVISION 



TX 605 



with some surprise, therefore, that we found the yeasts in the majority of the 
fins to be of the cultivated or brewery type. The anomaly was, however, ex 



f 



plained when we learned that next door to this particular cannery there was a 
Co factory actively engaged in producing ginger beer. Doubtless they were usin<: 
the brewery type of yeast, and in sufficient amount to charge the air <>t' the 
cannery. 

While the reason for the springing can be traced to air accompanied by micro- 
scopic life bein^ sucked into the tin while cooling, experience tells us that there is 
something more in it than can be explained by this theory. The "fly in the oint- 
ment " is this, that in the storage room about every second tin of pears shows 
signs of leaking, about every tenth tin of plums, and with peaches, apricots, and 
other stone fruits, the leaks are few in number. It is possible that the juice of 
pears has a greater solvent action upon the starch-luting of the container lid than 
other fruit juices. The subject is of interest, but there can be no doubt about the 
entry of life into the future springer subsequent to the cooking, and subsequent to 
the moment when the tins have cooled down to 170° F., or a little lower. The 
critical time begins when the tins are cold enough for the incoming yeast to be 
able to exist. Thus there is an appreciable interval between the time that the 
tins leave the cooker and the entry of potentially active micro-organisms. 

The fault is not always with the lid itself. Sometimes the tin plate is 
spongy, and the syrup oozes through the microscopic holes; at other times the 
solder cementing the cylindrical wall of the container splits when the metal is 
turned in the closing machine. Again, there may be a small hole left at the 
extreme end of the seam, where the metal has been cut to give a single thickness 
of metal for bending into the hooked joint. The weakness about the process is 
in the closing of the container. 

The remedy is theoretically simple. From the time that the tins are at 
170° F. until they are cold enough to work they should be in a sterile atmosphere. 
Then the edges of the tops and bottoms should be painted with a lacquer to close 
any microscopic opening. It is not a difficult proposition, and should be easy to 
accomplish in any cannery. 



>-)W > ' • ' "* 



By Authority: Albert J. Mullett, Government Printer, Melbourne. 



LIBRARY OF CONGRESS 




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